This proposal describes experiments that are concerned with the study of poliovirus replication and pathogenesis. An infectious viral cDNA clone will be mutagenized to create a collection of altered plasmids which will be used for most of the proposed studies. The functions of the central (P2) region of the genome and the 5'- and 3' -untranslated sequences will be addressed by studying viable virus mutants containing alterations in these regions. Mutated, noninfectious cDNAs which contain lesions in these areas of the genome will be studied by synthesizing positive strand RNA and transfecting this RNA into cultured cells. The role of terminal nucleotide sequences of the viral RNA in translation and replication will be studied using in vitro systems employing as templates mutated, subgenomic RNA fragments. Questions on the biology of poliovirus defective-interfering particles will be addressed. Positive strand RNAs will be synthesized which contain deletions in the capsid region, and these RNAs will be transfected into cells to determine whether DI RNAs can replicate, persist in and be rescued from mammalian cells. A mouse model for poliomyelitis will be studied to identify viral functions which participate in the production of paralytic disease. Mouse-avirulent viral mutants will be isolated and used to study the molecular basis of neurovirulence. The mouse model will also be used to identify viral capsid protein sequences required for entry of poliovirus into cells of the mouse central nervous system. To better understand how the viral capsid interacts with a cell during initiation of an infectious cycle, the cellular receptor for poliovirus will be studied. DNA transfection techniques will be used to isolate molecular clones of the cellular gene encoding the poliovirus receptor. These studies are part of our long-term research goal, to provide a complete description of the replication of a human pathogen.